Question Author
Right, I now have a better understanding of the situation.
I'm ashamed to say, I got the age of the child wrong, which is terrible because I was at his last birthday party. He's 2 not 5.
The father is using the fact that his ex is still in love with him. He was the one who cheated behind her back and he is blaming that on her mental health. She's a good mother and I'm not just saying that because she's our (me and my partners) friend. She does suffer from mental health issues but not to the extent that she is unable to maintain a relationship - she's is successfully bringing up a child whilst the father is at work.
This is my opinion, and only an opinion as I do not have children. The child is young and it's going to be confusing for him. Maybe she is jealous, I don't mind admitting that I would be jealous of his new relation, however I do not think that it is right for his father to tell his son to call this new woman, mum.
As he gets older, he'll understand, just like I did when I walked out of my own father. I'm concerned for my friend, what concerns me is that he is going to fight dirty and I honestly don't know if she can handle the stress. It's not going to be easy for me to tell her this and what makes it so much worse is that we're nearly 200 miles away from her (we're in Sheffield at the moment) and can't offer any support in person.
She threw his out of the house last night (he hasn't lived there for 2 months) and from what my partner has told me, she physically pushed him out the door. If she's not careful, she could end up losing custody, especially if she gets violent. He knows this and I do believe that he's setting her up, pulling her strings.
Apologies for the misinformation, not really a good start there. I was going to post it in CB however I decided against it. Thank you for all the replies, I'll keep you update. I have a feeling that this situation could turn really nasty.
Regards,
Stuart.